If u have a yellow discharge slight itching and a little swollen soreness in the vaginal area what is likely to cause that?

Discharge. There are several possibilities, including a yeast infection, bacterial vaginosis, and trichimonas (among others) -- this is best evaluated and managed by your doctor with a thorough exam and a wet mount.
Multiple Reasons. There are many reasons why this may be occurring. It could be a bacterial infection, and std, a yeast infection, menopause, chemical irritants. I would go see a doctor to help you figure out what it is so that this discomfort doesn't continue.